Recently, interests in an aerogel having excellent heat insulation properties have grown as industrial technologies are modernized. Aerogels developed to date may include an organic aerogel, such as resorcinol-formaldehyde or melamine-formaldehyde aerogel particles, and an inorganic aerogel including metal oxide such as a silica (SiO2), (Al2O3), titania (TiO2), or carbon (C) aerogel.
Among these aerogels, the silica aerogel is a highly porous material, wherein, since the silica aerogel may exhibit an excellent heat insulation effect by having high porosity and specific surface area as well as low thermal conductivity, applications in various areas, such as heat insulation materials, catalysts, sound-absorbing materials, fillers, and interlayer dielectric materials of a semiconductor circuit, are expected.
Since the silica aerogel has low mechanical strength due to its porous structure, the silica aerogel is normally commercialized in a form, such as an aerogel blanket or aerogel sheet, by compositing with a base material such as glass fibers, ceramic fibers, or polymer fibers. However, since the silica aerogel structurally contains 90 vol % or more of air in an internal pore, the silica aerogel has limitations in that scattering is severe during processing due to excessively low density and it is difficult to impregnate the silica aerogel into the base material. Also, since the silica aerogel is not mixed well due to an excessively large difference in density with respect to the base material even if a portion of the silica aerogel is impregnated, limitations, such as appearance defects and physical property deterioration, may occur. Furthermore, the silica aerogel must be mixed in a volume fraction of 50 vol % or more to achieve the heat insulation effect due to filling by efficiently blocking heat transfer, but it is not easy to process the powder itself at such a high mixing ratio.
Accordingly, in order to improve the properties of the aerogel, such as heat insulation, sound absorption, and catalytic activity, as well as processability of the silica aerogel or provide additionally required properties, a method of mixing an additive with the aerogel has been proposed. Specifically, a method of strengthening a structure and increasing density by introducing elements heavier than silicon (Si), such as titanium (Ti) and iron (Fe), into a silica aerogel skeleton by a method of adding the additive to a sol before polymerization of the silica aerogel or contacting the prepared silica aerogel with a liquid or vapor stream containing the additive, or a method of forming a composite with an inorganic material having a plate structure has been proposed.
However, convention methods have limitations in that control of size and particle size distribution of the additive materials is not easy, and deformation and reduction of the pore structure occur during the preparation of the silica aerogel.